1. Field of the Invention
The present invention relates to a pen-type or "marker" correction fluid applicator for applying a correction fluid to a print medium to mask markings on the print medium, and to an improved correction fluid formulation for cleaning and preventing clogging of the nib of a correction fluid applicator.
2. Description of the Related Art
Various pen-type or "marker" correction fluid applicator designs have been proposed for the purpose of conveniently applying correction fluid to a print medium, such as a paper surface, in order to mask or obscure handwritten, printed or photocopied markings formed on the paper surface. Such applicators typically include a correction fluid reservoir which stores the correction fluid in a liquid state and a delivery system which permits flow of the correction fluid onto the paper surface in a controlled manner.
For example, U.S. Pat. No. 4,923,317 to Bishop et al., the disclosure of which is incorporated herein by reference in its entirety, discloses a marker-type correction fluid applicator having an applicator tip designed to apply conventional correction fluid to a paper surface. The applicator includes a porous plastic or foam tip and a flow regulator disposed between the tip and a fluid reservoir. The regulator may be formed of a foam material or may include a pressure-actuated valve.
Other known marker-type correction fluid applicators, such as those disclosed in U.S. Pat. Nos. 5,277,510 to Okamoto et al., 5,338,775 to Matz et al., and 5,468,082 to Hori, the disclosures of which are incorporated herein by reference in their entireties, involve the use of spring-biased ball-type applicator tips. More specifically, the ball tip is biased axially outward by a spring valve to seal off flow of correction fluid from a reservoir. When the ball tip is pressed against a surface such as paper, the ball tip is displaced axially inward, thereby allowing correction fluid to flow from the reservoir, around the ball tip and onto the paper.
There has been an increasing interest in the field to formulate correction fluid systems that avoid separation of the liquid and solids of the correction fluid to prevent settling and agglomeration. To that end, thixotropic additives such as clays and bentones have been added to hinder separation and consequent hard coagulation of correction fluids. For example, the aforementioned patent to Matz et al. discloses a correction fluid formulation that is particularly suitable for ball-tip marker correction fluid applicators, wherein the correction fluid is formulated with thixotropic fluids designed to prevent the correction fluid from settling into constituent parts between uses, thereby eliminating the "nuisance" of needing to shake the fluid before use.
U.S. Pat. No. 5,368,810, the disclosure of which is incorporated herein by reference in its entirety, discloses a pen-type correction fluid dispenser having a squeezable tubular body which provides a greater degree of control over the amount of correction fluid dispensed. By pressing a spring-biased plunger against a surface, such as paper, a narrow opening is formed between the plunger and the surrounding wall by displacement of the plunger. The narrow opening is of a size that permits a sufficient flow of correction fluid from the tubular body to the paper only when the tubular body is simultaneously squeezed by the hand.
Attempts to produce pen or marker-type correction fluid dispensing applicators that employ fibrous nib delivery systems have been unsuccessful, because no correction fluid chemical formulations have addressed the problem of the correction fluid clogging the nib and drying on the nib between uses. Further, the need to develop a correction fluid formulated especially for a porous marker nib has not been recognized in the art. Commercially available nibs are typically composed of glued, thermally-bonded, axially-aligned polyester or like materials which are machined or shaped to provide contact points suitable for contacting a print medium, such as paper or other substrate. Typically, a substantially conical or frusto-conical shape is the most desirable shape for the point of the delivery nib of a correction fluid applicator, although other shapes may be utilized for specific applications. The nibs are hard enough so as not to substantially distort during use, but soft enough to provide a smooth application of correction fluid to the print medium.
In conventional use, nibs are designed to be saturated in highly pigmented formulations by being held in a loose plastic housing which allows fluid to flow over the outside of the nib, such that the nibs are not fed by capillary action. Capillary action has so far been successful only in low pigment or dye-based formulations. The reason for this lack of functionality of highly pigmented systems has been presumed to be that the pigments are too large in micron size to proceed through the nib. It has been suggested that lowering the particle size can solve the flow problem. Lowering particle size does provide for short term success; however, these correction fluid formulations rapidly stop working when strong solvents and highly cohesive resins swell the nib fibers and destroy the adhesives used in their manufacture. No known formulations provide a stable correction fluid utilizing weak resins and mild solvents.
A commercially viable correction fluid product must include a correction fluid that does not dry on the nib during repeated use or after short time without a cap. An additional requirement is that the fluid dry quickly, preferably no longer than approximately thirty seconds after application. Unfortunately, these criteria conflict, and existing correction fluid formulations that dry quickly on a print medium also tend to dry on the tip of the nib, thereby cutting off the flow of correction fluid. No formulations that dry quickly on a print medium have been found which do not also readily dry on the tip of the nib.
Another problem associated with correction fluid dispensing applicators is the need to prevent correction fluid from contacting the nib prior to the first use of the applicator by a customer. Attempts have been made to address this problem by employing spring valve systems within the applicator. However, such spring valve systems increase the complexity and cost of the applicator and have been found to be inconvenient.